#!/usr/bin/env julia

using Test

mutable struct Instruction
  cycles :: UInt
  add    :: Int
end

function parse_instruction_line(line)
  parts = split(line, limit=2)
  if parts[1] == "noop"
    return Instruction(1, 0)
  elseif parts[1] == "addx"
    return Instruction(2, parse(Int, parts[2]))
  else
    throw(DomainError("Unknown instruction: " * line))
  end
end

function signal_strength_sum(io; end_cycle=220)
  X :: Int = 1
  cycle :: Int = 1
  signal_strength_sum :: Int = 0
  next_test_cycle = 20
  for line in eachline(io)
    if mod(cycle - 20, 40) == 0 && cycle <= end_cycle
      println(cycle, " ", X)
      signal_strength_sum += cycle * X
      next_test_cycle += 40
    end
    inst = parse_instruction_line(line)
    new_cycle = cycle + inst.cycles
    if new_cycle > next_test_cycle
      signal_strength_sum += next_test_cycle * X
      next_test_cycle += 40
    end
    cycle = new_cycle
    X += inst.add
  end
  println("last inst cycle ", cycle)
  signal_strength_sum += X * sum(filter(x -> x >= cycle, 20:40:end_cycle))
  return signal_strength_sum
end

function get_crt(io; end_cycle=240)
  X :: Int = 2 # Note: add 1 to simplify 1-based indexing
  pending_instruction :: Union{Instruction, Nothing} = nothing
  screen = fill('.', (Int(ceil(end_cycle / 40)), 40))
  nrows, ncols = size(screen)
  for i in 1:nrows
    for j in 1:ncols
      if abs(X - j) <= 1
        screen[i, j] = "#"[1]
      else 
        screen[i, j] = '.'
      end

      if pending_instruction === nothing
        if eof(io)
          continue
        end
        inst = parse_instruction_line(readline(io))
        pending_instruction = inst
      end
      pending_instruction.cycles -= 1
      if pending_instruction.cycles == 0
        X += pending_instruction.add
        pending_instruction = nothing
      end
    end
  end
  return join(reduce(*, screen, dims=2, init=""), "\n")
end

function test()
  @testset "signal strength sum" verbose=true begin
    @test signal_strength_sum("example.txt") == 13140
    @test signal_strength_sum("input.txt") == 13220
  end
  @testset "crt test" verbose=true begin
    open("example.txt") do io
      @test get_crt(io) == chomp(read("example_crt.txt", String))
    end
    open("input.txt") do io
      @test get_crt(io) == chomp(read("input_crt.txt", String))
    end
  end
end

function main()
  if size(ARGS, 1) == 0
    test()
  else
    infile = ARGS[1]
    println("infile = ", infile)
    println("signal strength sum = ", signal_strength_sum(infile))
    open(infile, "r") do io
      println(get_crt(io))
    end
  end
end

main()